This invention relates to a distributor assembly for an internal combustion engine and, more particularly, to a distributor assembly in which a current flowing through a primary coil of an ignition coil is switched on and off by a primary current switching means of a control unit.
FIG. 6 is a sectional side view illustrating one example of a conventional distributor assembly for an internal combustion engine, in which reference numeral 1 designates a housing made of aluminum, 2 is a cap which has a plurality of circumferential electrodes 3 to be connected to spark plugs (not shown) of an internal combustion engine (not shown) and which covers an opening of the housing 1, 4 is an ignition coil disposed within the housing 1 and has primary and secondary coil (not shown) and an iron core (see FIG. 4). Reference numeral 5 designates a rotary shaft rotatably supported by the housing 1 and adapted to be connected to an engine crankshaft (not shown) for synchronous rotation therewith, 6 is a signal disc plate mounted to the rotary shaft 5 by means of a blank 7, 8 is a control unit mounted to the housing 1 and allows the rotary shaft 5 to extend therethrough. Although not every components are illustrated, the control unit 8 comprises a crankshaft angle sensor 12 which detects crankshaft rotational angle in relation to the signal disc plate 6 to output a crankshaft rotational angle signal to a control computer (not shown), a primary current switching means which is a power transistor for switching the primary coil current of the ignition coil 4 in response to the signal from the control computer (not shown) and a control circuit for controlling the operation of the power transistor. Reference numeral 9 is a rotor securely mounted to the blank 7 for rotation therewith for distributing a secondary high voltage output from the ignition coil 4 to the circumferential electrodes 3 in synchronization with the rotation of the engine crankshaft, 10 is a cover which is an integral combination of a resin layer for preventing voltage leakage from the high-tension distribution region and a shield for suppressing noise generated by spark discharge in the high-tension distribution region, 11 is a seal member disposed between the cap 2 and the housing 1. In order to fixedly support the ignition coil 4 in the housing 1, a support plate 16 extending over a substantial portion of the top surface of the ignition coil 4 is securely mounted to the housing 1 by means of screws 17.
FIG. 7 is a plan view o the conventional distributor assembly illustrated in FIG. 6 but with the cap 2, the rotor 9 and the cover 10 removed. Reference numeral 13 designates a control unit connector integrally molded on the control unit 8 for transmitting a signal from the control computer to the control circuit and for supplying drive voltages to the power transistor and the crankshaft angle sensor unit 12, 14 is an ignition coil connector mounted to the housing 1 through a seal 19, and 15 are exposed terminals for connecting the primary coil of the ignition coil 4 to an external power source (not shown).
When the rotary shaft 5 is rotated as the engine crankshaft rotates, the signal disc plate 6 is also rotated to intermittently interrupt the light beam in the crankshaft angle sensor 12, upon which the crankshaft angle sensor 12 provides to the control computer an output signal indicative of the crankshaft rotational speed and position in response to the frequency of the intermittent light beam. The power transistor switches on and off the primary current of the ignition coil 4 in accordance with the signal from the control computer so that the secondary voltage is generated in the ignition coil 4 at the ignition timing. This secondary voltage is sequentially distributed to the circumferential electrode 3 as the distributor rotor 9 rotates, so that the spark plugs of the engine are sequentially ignited to keep the engine running.
In the conventional distributor assembly as above described, in order to protect the ignition coil 4 and the control unit 8 from dust and moisture, they are placed within the relatively large and heavy housing 1. However, since the housing is heavy and large in radial dimension, the distributor assembly is inevitably large and heavy. Also, since the housing 1 is made of aluminum, a large potential difference may be generated between the electrically conductive housing and the ignition coil 4 and a discharge spark may generate therebetween.
Also, since the ignition coil connector 14 is an individual member mounted to the housing 1 and the external source connector 15 is exposed to the exterior of the distributor housing 1, number of the parts is relatively large resulting in difficult assembly and poor resistance to moisture and the exposed wire connection. Also, the radially extending connectors 14 and 15 project from the housing 1 for a relatively large distance, thus increasing the overall radial dimension of the distributor assembly.
Further, since the ignition coil 4 is supported in the housing 1 by means of the support plate 16 and the screws 17, the number of components is relatively large, the assembled distributor is heavy and relatively expensive.